Multiple textures for one mesh
Add a new UV set in the Properties panel , and unwrap the mesh in Edit mode using that UV set. Open a new image texture in the UV Image Editor at the size you want the final to be, and in the Render tab of the Proiperties panel, open up the Bake tab. Select 'Textures' and then press 'Bake', and you should see your existing textures from the object appear in the new image. Save it, and then set it in the material's texture stack for actual use.